The ongoing search for increased aircraft engine performance had prompted materials science engineers to investigate intermetallic compounds as replacement materials for nickel and cobalt base superalloys currently in widespread use in gas turbine engines. Of particular interest over the past decade has been gamma or near-gamma titanium aluminides because of their low density and relatively high modulus and strength at elevated temperatures.
Modifications have been made to the titanium aluminide composition in an attempt to improve the physical properties and processability of the material. For example, the ratio of titanium to aluminum has been adjusted and various alloying elements have been introduced in attempts to improve ductility, strength, and/or toughness. Moreover, various processing techniques, including thermomechanical treatments and heat treatments have been developed to this same end.
The latest alloy to be developed is disclosed in Larsen, Jr. et al., U.S. Pat. No. 5,350,466. Larsen et al. describe a titanium aluminide alloy composition consisting essentially of, in atomic percent, 44 to 49 Al, 0.5 to 4.0 Nb, 0.25 to 3.0 Mn, 0.1 to less than 1.0 W, 0.1 to less than 1.0 Mo, 0.1 to 0.6 Si, and the balance Ti. The alloy in U.S. Pat. No. 5,350,466 is superior to the other alloys in creep as claimed in the patent for the class of gamma titanium aluminides with reasonable room temperature ductility (e.g.,&gt;0.5% elongation).
The present invention provides a titanium aluminide material alloyed with certain selected alloying elements in certain selected proportions that Applicants have discovered yields a further improvement in creep resistance than the alloy in U.S. Pat. No. 5,350,466, and additionally provides high temperature strength significantly exceeding the alloy of U.S. Pat. No. 5,350,466.